The Compressor/Fan junction allows you to model the pressure added to a system by a compressor, and model many transient events involving compressors/fans. Because all compressors/fans are different, AFT xStream does not provide any standard types. Pressure and flow data that describes the device must be obtained from the manufacturer or from test data. To reduce repeated data entry, frequently-used compressors/fans can be added to the Junction Library.

Common Input Information

Like all junctions, Compressor/Fan junctions require a junction number, junction name, and inlet and outlet elevations. Similar to other junctions, compressors can have Design Alerts and Notes applied to them. They require two connecting pipes. Note that the direction of the connected pipes define which side of the compressor/fan is suction and which is discharge.

Compressor Model

This tab requires the selection and definition of what type of compressor/fan the junction represents. There are two models currently available:

• Centrifugal (Rotodynamic)- Represents a typical centrifugal compressor where the head added to the fluid is related to the flow through the compressor via a compressor curve.

• Positive Displacement - Represents a steady state approximation of a positive displacement compressor. The flow is fixed to a constant value, and whatever head is necessary to obtain that flow will be supplied.

Variable Speed

This tab allows the speed of the compressor to vary. These options are only available for a centrifugal compressor.

• Fixed Speed (%) - Directly modify the compressor curve according to the Affinity Laws. The Compressor/Fan Curve entered in Compressor/Fan Configuration is always assumed to be the 100% speed curve.

Transient

The Compressor/Fan junction allows for Speed vs Time transients. This allows the user to directly specify how the speed of the compressor/fan changes over time. This can be used to model startups, trips, or control transients.

For more information on transient data, including event transients, see Junction Transient Data.

All of the transient options need to know when to start with Initiation of Transient and allow the definition of a Transient Special Condition.

Optional

There are several optional parameters that can be defined for a compressor/fan. Some of these are available to most junctions such as Display on Workspace, and Workspace Icon.

Also present are several compressor junction specific options:

• Special Condition

• None - The compressor/fan operates normally.

• Compressor Off No Flow - The compressor/fan is shut off and blocked. This is identical to a closed valve.

• Compressor Off With Flow Through - The compressor/fan is shut off but allows flow to continue through. This is identical to a lossless connection.

Additionally, there is the option to insert the efficiency data of the compressor/fan motor.

Related Blogs

Modeling Fans, Blowers and Compressors - Oh My!